One approach to the problem of active noise control is described in "A Multiple Error LMS Algorithm and its Application to the Active Control of Sound and Vibrations," S. J. Elliott, I. M. Strothers, and P. A. Nelson, IEEE Transactions on Acoustics, Speech and Signal Processing, Vol. ASSP-35, No. 10, October 1987, pp. 1423-1434. A second approach is described in U.S. Pat. No. 5,091,953, issued to S. Tretter.
The article by Elliott et al. describes a time-domain approach in which a single reference signal derived from the noise source is passed through N.sub.a FIR filters whose taps are adjusted by an adaptive LMS algorithm. The approach assumes that the matrix of impulse responses relating the actuator and sensor signals are known. However, it is often difficult, in practice, to provide accurate estimates of these impulse responses. The Elliott et al. article does not offer any guidance for making these estimates.
U.S. Pat. No. 5,091,953 describes a cancellation arrangement using the well-known adaptive LMS algorithm to determine the optimal control signals to be sent to the actuators for each harmonic in the noise to be cancelled. However, this arrangement is limited in application to repetitive phenomena.